1. Field of the Invention
This invention relates to the art of constructing internal combustion engines and particularly to the construction of the combustion chamber, valve train chamber, and crankcase chamber for such engines.
2. Description of the Prior Art
Substantially all commercial engine housings are made as metal castings. In making cast metal engine housings for automobiles, it is conventional to split the housing configuration along a horizontal plane to define a separate cylinder block and a separate head, both pieces being clamped together under high force with an intervening gasket therebetween to assure combustion gas and water tightness. These clamping forces are substantial and are implemented usually by use of several long bolts which extend from the head into deep threaded bores of the block. The forces must be sufficiently great to withstand the separating forces caused primarily by gas pressure in the combustion chambers. The great clamping forces in turn may cause slight distortion of the roundness of the cylinder bores and straightness of the valve guides, which translates into higher frictional forces because ring forces must be increased to distort the rings to accommodate out-of-roundness and higher frictional forces against valve stems during reciprocal movement. The engine durability may be adversely affected over long usage.
Making engine housings to mate along a horizontal surface demands that considerable coring be used to define internal passages that do or do not interface with the horizontal mating surface; the cored passages not being directly accessible to cleaning and removal of casting fins or debris. Moreover, techniques of making such cast blocks and heads require that certain other passages be separately machined after the castings are complete, which adds considerable cost to the manufacture of such items. Increased weight is undesirable from a fuel economy standpoint. Thus, it can be seen that the horizontally split engine construction is in need of some improvement in the areas of weight, cost, quality, automation and effect on engine performance.
Some attempt has been made to reduce weight in such horizontally split engines by substituting cast aluminum for all or part of the cast iron housing portions. But aluminum suffers from an inability to withstand wear at high temperatures and abrasive wear in a manner equivalent to that of cast iron so that numerous inserts of improved properties must usually be provided at points where excessive wear would occur. Aluminum is also less likely to withstand the problem of undue clamping forces. Automating the assembly of a horizontally split engine has not proved to be entirely satisfactory because several subassemblies of such horizontally split engine must be cradled in separately defined journals, yokes and supports which in turn must be separately mounted and separately assembled, complicating the steps of assembly and inhibiting assembly robotically.